One piece snap fit acetabular cup

ABSTRACT

A joint prosthesis comprising an acetabular cup comprising at least a first and a second load carrying member, the first load carrying member being substantially more shock absorbing and resilient that the second load carrying member.

This application is a continuation of U.S. Non-Provisional applicationSer. No. 10/289,126, filed on 5 Nov. 2001, U.S. Non-Provisionalapplication Ser. No. 09/902,701, filed 5 Sep. 2001, U.S. Non-Provisionalpatent application Ser. No. 09/043,076, filed Feb. 2, 1999, which claimsbenefit of 35 U.S.C. § 119(e) of Israeli Patent Application No.: 115168,filed 04 Sep. 1995, the contents of which are incorporated herewith byreference in their entirety.

FIELD OF THE INVENTION

The present invention relates to apparatus and methods for Jointprosthesis surgery generally.

Joint prostheses are well known in the art. Generally joint prosthesesinclude a metal portion, typically constructed of steel or titanium,which articulates with a bony portion of the body. Non-articulatingportions of the prosthesis are generally fixedly attached to tissue orbone. For example, a hip joint prosthesis of the art generally includesa metallic femoral head which articulates with a portion of the hipbone, and a metallic stem which is fixedly attached to the femur.

Several problems are associated with prostheses of the art, for example,due to the mismatch between material properties of the prosthesis andbone. The contact between metal and bone may cause fretting wear of thebone. The difference in coefficient of thermal expansion between metaland bone may cause discomfort to the patient, especially during weatherchanges. The metallic prosthesis provides virtually no shock absorptionor damping.

It is known that a bone grows or regenerates according to the stresswhich it must bear. The metal prosthesis generally bears a much largerportion of weight than the surrounding bone. The reduced stress on thesurrounding bone may tend to contribute to degeneration and recession ofthe bone, and to create an undesirable gap between the bone and theprosthesis.

In order to overcome the aforementioned problems, a great variety ofprostheses with resilient portions have been proposed and developed. Thefollowing U.S. patents are believed to be representative of the art:U.S. Pat. Nos. 5,522,904, 5,514,184, 5,514,182, 5,507,836, 5,507,833,5,507,830, 5,507,823, 5,507,820, 5,507,818, 5,507,814, 5,491,882,5,489,311, 5,458,651, 5,458,643, 5,448,489, 5,425,779, 5,415,662,5,405,411, 5,405,403, 5,389,107, 5,387,244, 5,376,125, 5,376,064,5,370,699, 5,358,525, 5,344,459, 5,336,268, 5,330,534, 5,326,376,5,316,550, 5,314,494, 5,314,493, 5,314,478, 5,290,314, 5,282,868,5,222,985, 5,217,499, 5,217,498, 5,201,882, 5,201,881, 5,197,989,5,197,987, 5,181,925, 5,171,276, 5,156,631, 5,151,521, 5,147,406,5,146,933, 5,133,763, 5,116,374, 5,108,451, 5,108,446, 5,080,677,5,049,393, 5,041,140, 5,019,107, 5,002,581, 4,997,447, 4,963,154,4,963,153, 4,955,919, 4,955,912, 4,950,298, 4,938,773, 4,938,771,4,936,856, 4,919,678, 4,919,674, 4,908,035, 4,904,269, 4,888,020,4,822,365, 4,813,962, 4,808,186, 4,795,474, 4,795,470, 4,715,859,4,664,668, 4,662,889, 4,661,112, 4,570,270, 4,344,193 and 3,875,594.

The present invention seeks to provide improved joint prostheses which,inter alia, help overcome the above mentioned problems of the prior art.

The prostheses provide shock absorption, damping and resiliency.Portions of the prostheses which interface with human tissue arepreferably constructed of resilient materials which are compatible withhuman bone or tissue, such as certain types of polyurethane. Certainportions of the prostheses may be constructed of composite materialswhose mechanical or physical properties may be optimized, such as tomatch properties of the local human bone or tissue. By matchingproperties of the local bone or tissue, the prosthesis behavesmechanically, structurally and thermally in a manner similar to thelocal bone or tissue, which helps make the prosthesis more efficient andcomfortable.

An important feature of the prostheses is that they help distributestresses optimally, thereby stimulating regeneration of bone.

The present invention is applicable for any joint in which there is freemovement, known in technical terms as a true diarthrosis. Truediarthroses include:

-   -   1. Gliding joints, known as arthrodias, in which the surfaces of        the joint are flat, such as in the carpal bones;    -   2. Hinge Joints, known as ginglymi, such as the knee or elbow;    -   3. Condyloid joints, known as condylarthroses, which allow        flexion, extension and lateral movement, but no rotation, such        as the wrist, and saddle-shaped joints which allow the same type        of movement as condyloid joints, but are generally stronger,        such as the carpo-metacarpal joint of the thumb;    -   4. Ball and socket joints, known as enarthroses, such as the hip        and the shoulder; and    -   5. Pivot joints, known as trochoides, which only allow rotation,        such as the radio-ulnar joints.

The present invention will be described in detail hereinbelow withrespect to a prosthesis for an enarthrosis, such as the hip joint, andto a prosthesis for a ginglymus, such as the knee joint. It isappreciated, however, that a prosthesis for any true diarthrosis is inthe scope of the present invention.

In a radical departure from the prior art, and in accordance with oneembodiment of the present invention, a hip joint prosthesis is providedwhich includes an artificial femoral head which is not fixedly attachedto the femur, but rather articulates with both the femur and theacetabulum. The artificial femoral head is generally spherical and mayabsorb shocks, provide damping and/or be resilient. A separate,artificial femoral head is easier to insert than the prostheses of theprior art which have a stem.

In addition, the artificial femoral head may be provided with delimitingrails or grooves which serve to define and limit the movement paths ofthe femur with respect to the body, if required, and dislocation of thejoint is substantially prevented. The delimiting rails or grooves mayalso serve as bumpers which damp and cushion the femoral head at thelimits of its articulation.

The prostheses of the present invention may also be provided withpassageways for fluid, such as synovial fluid. Fluid present in thesepassageways helps to lubricate the prosthesis and provides viscousdamping.

Since the prostheses of the present invention are resilient, theygeometrically adapt themselves to changes in static and dynamic forcesborne by the joint. In the case of the hip joint prosthesis of thepresent invention, for example, normal raising of the thigh does notapply substantial forces on the hip joint, and the resilient hip jointprosthesis allows the freedom of movement of a ball and socket Jointwith substantially no deformation nor obstruction to movement due tofriction between the prosthesis and human tissue or bone, or betweenadjacent regions of the prosthesis, such as between the artificialfemoral head and an artificial socket.

In contrast, when the person is standing, the static force of the weightof the person on the hip joint causes the resilient prosthesis to deformsomewhat, i.e., to be squashed a certain amount. This deformationprovides a relatively larger area for supporting the weight on thejoint, thereby reducing pressure on the joint. The deformation alsoincreases the friction force between the prosthesis and human tissue orbone, or between adjacent regions of the prosthesis, such as between theartificial femoral head and an artificial socket. The increased frictionis beneficial because it does not hinder the stationary person; on thecontrary, the increased friction increases stability of the person.

The resiliency of the prosthesis is also beneficial during sudden slipsor falls. The dynamic and/or static forces due to the sudden movementtend to deform or squash the resilient prosthesis. As described above,the deformation reduces pressure on the joint, reduces danger of theprosthesis detaching from the bone, and increases friction which helpsprovide stability during the slip or fall.

There is thus provided in accordance with a preferred embodiment of thepresent invention, a joint prosthesis including at least a first and asecond load carrying member, the first load carrying member beingsubstantially more shock absorbing and resilient than the second loadcarrying member.

In accordance with a preferred embodiment of the present invention, atleast one of the load carrying members is characterized in having atleast one of strength and elasticity generally similar to that of humancartilage.

There is also provided in accordance with a preferred embodiment of thepresent invention, a joint prosthesis including a plurality ofalternating adjacent portions of substantially rigid and substantiallyresilient materials.

There is also provided in accordance with a preferred embodiment of thepresent invention, a joint prosthesis including a plurality ofalternating adjacent first and second portions, the first portion havinga substantially rigid configuration and the second portion having asubstantially resilient configuration.

Preferably at least one of the first and the second portions isgenerally omega shaped. The joint prosthesis may include at least oneportion compatible with human tissue. The joint prosthesis may have atleast one hollow portion.

Preferably, any of the joint prostheses includes at least one delimitingrail or groove.

Preferably, any of the joint prostheses includes at least one passagewayfor a fluid.

There is also provided in accordance with a preferred embodiment of thepresent invention, a hip joint prosthesis including an artificial,spherical femoral head which is adapted to articulate with an acetabulumand an upper portion of a thigh.

There is also provided in accordance with a preferred embodiment of thepresent invention, a hip joint prosthesis including an artificial,self-articulating femoral head, the head being attachable to at leastone of an acetabulum and an upper portion of a thigh.

Preferably, the hip joint prosthesis includes an artificial femoral headwhich is shock absorbing, provides damping and/or is substantiallyresilient.

Preferably, the femoral head has at least one hollow portion.

Further in accordance with a preferred embodiment of the presentinvention, the hip joint prosthesis also includes an artificialacetabulum attachable to an innominate bone, the artificial femoral headarticulating with the artificial acetabulum.

Still further in accordance with a preferred embodiment of the presentinvention, the hip joint prosthesis also includes an artificial femoralsocket attachable to a femur, the artificial femoral head articulatingwith the artificial femoral socket.

Further in accordance with a preferred embodiment of the presentinvention, the artificial femoral head includes a device forsubstantially preventing dislocation of the artificial femoral head fromthe artificial acetabulum, the artificial femoral socket, or both.

Preferably the device for substantially preventing dislocation is shockabsorbing or resilient.

Further in accordance with a preferred embodiment of the presentinvention, the artificial femoral head includes at least one delimitingrail or groove. The delimiting groove may have a different geometricalshape than that of the rail. This permits providing variouspredetermined ranges and paths of motion.

Still further in accordance with a preferred embodiment of the presentinvention, the artificial femoral head has at least one passageway for afluid.

Additionally in accordance with a preferred embodiment of the presentinvention, the hip joint prosthesis includes a sleeve which envelops atleast one portion of the prosthesis and which is attachable to at leastone of a portion of an innominate bone and a thigh. Preferably thesleeve includes a relatively high strength fabric.

Further in accordance with a preferred embodiment of the presentinvention, the artificial femoral socket is adapted to fit substantiallysnugly with at least one upper portion of a femur.

Still further in accordance with a preferred embodiment of the presentinvention, the artificial femoral head includes a plurality ofalternating adjacent portions of substantially rigid and substantiallyresilient materials.

Additionally in accordance with a preferred embodiment of the presentinvention, the hip joint prosthesis further includes a stem insertableinto a femur.

Further in accordance with a preferred embodiment of the presentinvention, the hip joint prosthesis includes an outer layer attachableto a femur, the outer layer including a material compatible with humantissue.

There is also provided in accordance with a preferred embodiment of thepresent invention, a knee joint prosthesis including a femoral portionand a tibial portion, the femoral portion being attachable to a femurand the tibial portion being attachable to a tibia, the femoral portionarticulating with the tibial portion, wherein at least one of thefemoral portion and the tibial portion is shock absorbing, providesdamping or is substantially resilient.

In accordance with a preferred embodiment of the present invention, theknee joint prosthesis includes a device operative to limit motion or thetibia with respect to the femur.

Preferably, the device operative to limit motion of the tibia withrespect to the femur, is shock absorbing.

Additionally in accordance with a preferred embodiment of the presentinvention, the femoral portion is generally convex and the tibialportion is generally concave.

Alternatively in accordance with a preferred embodiment of the presentinvention, the femoral portion is generally convex and the tibialportion is generally convex.

Further in accordance with a preferred embodiment of the presentinvention, the knee joint prosthesis includes at least one rollerelement, the femoral portion articulating with the tibial portion viathe at least one roller element.

Preferably, the knee joint prosthesis has at least one fluid passageway.

There is also provided in accordance with a preferred embodiment of thepresent invention, a bone fastener including a plurality of alternatingadjacent portions of substantially rigid and substantially resilientmaterials.

There is also provided in accordance with a preferred embodiment of thepresent invention, a bone fastener including a plurality of alternatingadjacent first and second portions, the first portion having asubstantially rigid configuration and the second portion having asubstantially resilient configuration.

There is also provided in accordance with a preferred embodiment of thepresent invention, a method of incision of a ligament including forminga substantially wave-like incision in the ligament.

There is also provided in accordance with a preferred embodiment of thepresent invention, a method of insertion of a hip joint prosthesisincluding:

-   -   fixedly attaching a first joint element to an upper portion of a        femur, the first joint element fitting substantially snugly with        the upper portion of the femur;    -   fixedly attaching a second joint element to a portion of an        innominate bone; and    -   inserting an artificial femoral head intermediate the first and        the second joint elements, such that the artificial femoral head        articulates with at least one of the first and the second joint        elements.

Preferably, one or more natural or artificial ligaments may be used tostrengthen the hip joint.

There is also provided in accordance with a preferred embodiment of thepresent invention, a method for limiting a range of movement of a hipjoint including:

-   -   implanting a hip joint prosthesis comprising at least one        delimiting rail and at least one delimiting groove, the at least        one delimiting rail articulating with the at least one        delimiting groove, such that the at least one delimiting groove        limits articulation of the at least one delimiting rail therein.

The present invention will be understood and appreciated from thefollowing detailed description, taken in conjunction with the drawingsin which:

FIG. 1 is a simplified illustration of a human hip joint;

FIG. 2 is a simplified illustration of a hip joint prosthesis,constructed and operative in accordance with a preferred embodiment ofthe present invention;

FIG. 3 is a partially sectional illustration of the hip joint prosthesisof FIG. 2;

FIG. 4 is a partially sectional illustration of the hip joint prosthesisof FIG. 2, wherein the femur is rotated laterally;

FIG. 5 is a partially sectional illustration of the hip joint prosthesisof FIG. 2, wherein the femur is rotated rearwardly;

FIG. 6 is a simplified pictorial illustration of an artificial femoralhead of the hip joint prosthesis of FIG. 2, the femoral head comprisingtwo delimiting rails;

FIGS. 7A and 7B are simplified illustrations of an artificial femoralhead, constructed and operative in accordance with another preferredembodiment of the present invention, articulating with artificial andnatural acetabula respectively, and wherein the artificial femoral headhas no delimiting rails;

FIGS. 8A and 8B are simplified illustrations of an artificial femoralhead fixedly attached to a stem, constructed and operative in accordancewith yet another preferred embodiment of the present invention,articulating with artificial and natural acetabula respectively, andwherein the artificial femoral head has no delimiting rails;

FIG. 8C is a simplified illustration of an artificial, self-articulatingfemoral head fixedly attached to a stem and to an acetabulum,constructed and operative in accordance with a preferred embodiment ofthe present invention;

FIG. 9A is a simplified pictorial illustration of an artificial femoralhead and an artificial acetabulum, constructed and operative inaccordance with still another preferred embodiment of the presentinvention, and wherein the artificial femoral head has one delimitingrail which articulates with the generally elliptically shapedacetabulum;

FIG. 9B is a simplified sectional illustration of the femoral head ofFIG. 9A, taken along lines 9B-9B in FIG. 9A;

FIG. 9C is a simplified pictorial illustration of a flexible and stablebone connector, constructed and operative in accordance with a preferredembodiment of the present invention;

FIGS. 9D and 9E are simplified, sectional illustrations of a flexibleand stable bone connector stem of a hip joint prosthesis, constructedand operative in accordance with a preferred embodiment of the presentinvention, before and after deployment, respectively;

FIGS. 9F and 9G are simplified, sectional illustrations of a flexibleand stable bone connector stem of a hip joint prosthesis, constructedand operative in accordance with another preferred embodiment of thepresent invention, before and after deployment, respectively;

FIG. 10 is a simplified sectional illustration of a non-hollowartificial femoral head, constructed and operative in accordance with apreferred embodiment of the present invention;

FIG. 11 is a simplified sectional illustration of an artificial femoralhead, constructed and operative in accordance with another preferredembodiment of the present invention, and wherein the femoral headcomprises a plurality of hollow portions;

FIG. 12 is a simplified sectional illustration of an artificial femoralhead, constructed and operative in accordance with yet another preferredembodiment of the present invention, and wherein the femoral headcomprises a plurality of hollow portions filled with a fluid;

FIG. 13 is a simplified sectional illustration of an artificial femoralhead, constructed and operative in accordance with still anotherpreferred embodiment of the present invention, and wherein the femoralhead comprises a plurality of portions, each portion not necessarilyhaving the same mechanical or physical properties;

FIG. 14A is a simplified sectional illustration of an artificial femoralhead, constructed and operative in accordance with another preferredembodiment of the present invention, and wherein the femoral headcomprises a protruding delimiting bumper;

FIG. 14B is a simplified sectional illustration of an artificial femoralhead, constructed and operative in accordance with yet another preferredembodiment of the present invention, and wherein the femoral headcomprises a thin, resilient outer shell and a resilient core;

FIG. 15 is a simplified pictorial illustration of an artificial femoralhead, constructed and operative in accordance with a preferredembodiment of the present invention, and including delimiting grooves;

FIG. 16 is a simplified sectional illustration of an artificial femoralhead, constructed and operative in accordance with another preferredembodiment of the present invention, and wherein the femoral head hasfluid passageways;

FIG. 17 is a simplified sectional illustration of an artificial femoralhead, constructed and operative in accordance with yet another preferredembodiment of the present invention;

FIGS. 18A and 18B are simplified pictorial and sectional illustrationsrespectively of an artificial femoral head, constructed and operative inaccordance with another preferred embodiment of the present invention,and wherein the femoral head comprises a plurality of alternatingadjacent portions of substantially rigid and substantially resilientmaterials, FIG. 18B being taken along lines 18B-18B in FIG. 18A;

FIGS. 18C-18F are simplified pictorial illustrations of alternativeconstructions of a femoral head including a plurality of alternatingadjacent-portions of substantially rigid and substantially resilientmaterials;

FIG. 18G is a simplified pictorial illustration of an artificialacetabulum, constructed and operative in accordance with a preferredembodiment of the present invention;

FIGS. 18H, 18I and 18J are simplified illustrations of installing theartificial acetabulum of FIG. 18G into a natural acetabulum, inaccordance with a preferred embodiment of the present invention;

FIGS. 18K and 18L are simplified sectional illustrations of twoartificial acetabula, constructed and operative in accordance with twopreferred embodiments of the present invention;

FIGS. 19A-19C are simplified pictorial illustrations of a method ofincision of ligaments, such as prior to insertion of a hip jointprosthesis, in accordance with a preferred embodiment of the presentinvention;

FIG. 20 is a simplified pictorial illustration of a sleeve for joining afemoral head with the innominate bone, constructed and operative inaccordance with a preferred embodiment of the present invention;

FIG. 21 is a simplified sectional illustration of an expandableartificial femoral head, constructed and operative in accordance with apreferred embodiment of the present invention;

FIG. 22 is a simplified illustration of a human knee joint;

FIGS. 23 and 24 are respective simplified side and front viewillustrations of a knee joint prosthesis, constructed and operative inaccordance with a preferred embodiment of the present invention;

FIG. 25 is a simplified illustration of a femoral portion of the kneejoint prosthesis of FIGS. 23 and 24;

FIG. 26 is a simplified illustration of a tibial portion of the kneejoint prosthesis of FIGS. 23 and 24;

FIGS. 27 and 28 are respective simplified side and front viewillustrations of a knee joint prosthesis, constructed and operative inaccordance with another preferred embodiment of the present invention;

FIGS. 29 and 30 are respective simplified side and front viewillustrations of a knee joint prosthesis, constructed and operative inaccordance with yet another preferred embodiment of the presentinvention;

FIGS. 31 and 32 are respective simplified side and front viewillustrations of a knee joint prosthesis, constructed and operative inaccordance with still another preferred embodiment of the presentinvention;

FIG. 33 is a simplified illustration of a roller element included in theknee joint prosthesis of FIGS. 31 and 32;

FIG. 34 is a simplified, partially sectional illustration of a bonefastener, constructed and operative in accordance with a preferredembodiment of the present invention; and

FIG. 35 is a simplified, partially sectional illustration of a vertebrareplacement, constructed and operative in accordance with a preferredembodiment of the present invention.

The present invention will now be described in detail with respect to aprosthesis for an enarthrosis, an example being the hip joint, and to aprosthesis for a ginglymus, an example being the knee joint. It isappreciated, however, that a prosthesis for any true diarthrosis is inthe scope of the present invention.

For a better understanding of a hip joint prosthesis, a basicdescription of the human hip joint is presented here with reference toFIG. 1, which illustrates the hip of the right side of the body. The hipjoint is a ball and socket joint, the ball being the femoral head (headof the thigh bone) which articulates with the acetabulum of theinnominate bone, known in non-technical terms as the socket of the hipbone.

The innominate bone in the area of the hip joint is made of threeportions: the upper portion is called the ilium, the middle portion iscalled the pubis and the lower portion is called the ischium. Thefemoral head is connected to the innominate bone by a plurality ofligaments. The ligaments shown in FIG. 1 are the ilio-femoral ligamentsand the pubo-femoral ligament. There is also an ischio-femoral ligament,not seen in FIG. 1. The femoral head articulates with a fibrous rim ofthe acetabulum called the cotyloid ligament.

Generally a hip joint replacement of the prior art involves replacingthe natural femoral head with a metallic artificial femoral head whichis fixedly attached to a stem. The stem is generally inserted in thefemur and the femoral head articulates with the acetabulum, if stillintact, or some other depression, artificial or natural, in theinnominate bone. Some or all of the ilio-femoral, pubo-femoral andischio-femoral ligaments may be removed to provide access to the femoralhead and acetabulum.

Reference is now made to FIGS. 2 and 3 which illustrate a hip jointprosthesis 10, constructed and operative in accordance with a preferredembodiment of the present invention. In a radical departure from theprior art, hip joint prosthesis 10 comprises a femoral head 12 which isnot fixedly attached to the femur, but rather is capable of articulatingwith both the thigh and the innominate bone. In accordance with apreferred embodiment of the present invention, femoral head 12 may beconstructed of a rigid material compatible with human tissue, forexample, a metal such as stainless steel, or a structural plastic.

In accordance with another preferred embodiment of the presentinvention, artificial femoral head 12 is constructed of a material whichis shock absorbing, and additionally or alternatively provides damping,and additionally or alternatively is resilient. An example of such amaterial is polyurethane or synthetic rubber.

A resilient artificial femoral head, unlike the prior art, yields uponapplication of forces and substantially returns to its original shapeafter such forces are removed.

Artificial femoral head 12 is preferably, although not necessarily,generally spherical in shape. In accordance with a preferred embodimentof the present invention, and as shown in FIG. 3, femoral head 12 has ahollow core 14. Hollow core 14, inter alia, adds to the resiliency andshock absorbing characteristics of femoral head 12.

In accordance with a preferred embodiment of the present invention, hipjoint prosthesis 10 also comprises an artificial acetabulum 16 which ispreferably fixedly attached to the innominate bone via an acetabuluminterface 18. Artificial femoral head 12 articulates with artificialacetabulum 16.

Additionally in accordance with a preferred embodiment of the presentinvention, hip joint prosthesis 10 comprises an artificial femoralsocket 20 which is preferably fixedly attached to the femur via a stem22. Alternatively, socket 20 may be attached to the femur without astem, for example, by bonding. Artificial femoral head 12 articulateswith artificial femoral socket 20. Socket 20 is shaped to facilitatethis articulation, such as being generally concave. In addition, socket20 is preferably shaped to overlap, or snugly fit, the upper portion ofthe natural femur. The generally concave, overlapping shape ofartificial femoral socket 20 helps distribute stresses optimally on thefemur, thereby stimulating regeneration or bone.

Socket 20 may overlap and “hug” the upper portion of the femur on theoutside surface of the femur. Alternatively or additionally, socket 20may be configured to fit snugly into an inner surface of the femur.

It is important to note that socket 20 serves two general tasks, asdescribed above. The first task is articulation with artificial femoralhead 12. The second task is fitting snugly with the femur anddistributing stresses evenly thereon.

It is appreciated that in accordance with another preferred embodimentof the present invention, socket 20 may comprise two separate portionseach generally dedicated to serving one of the above described tasks. Afirst portion 20A, generally concave in shape, may be generallydedicated to articulation with artificial femoral head 12. A secondportion 20B, generally shaped as a “crown” to hug and snugly fitcircumferentially around and on top of the femur, may be generallydedicated to distributing stresses evenly on the femur. This is true ofany of the sockets described herein with reference to any of theembodiments of the present invention. The “crown”, i.e., second portion20B, greatly changes the loading conditions of prosthesis 10, decreasesstresses exerted on the femur by stem 22, and creates a new andhealthier stress distribution on the surrounding bone and tissue. Withthe support of second portion 20B, stem 22 may have a much smallersection throughout and particularly at its neck.

Stem 22 preferably includes a core 24 and an outer layer 26, as seen inFIGS. 2 and 3. Outer layer 26 preferably includes one or more ridges 28,which, inter alia, help distribute stresses and help fasten stem 22 tothe femur.

Core 24 of stem 22, artificial acetabulum 16 and artificial femoralsocket 20 are preferably constructed of a rigid material, for example,stainless steel or a structural plastic. Alternatively, the rigidmaterial may be a composite material, such as a lay-up of graphitefibers, which may be constructed to have mechanical or physicalproperties, such as modulus of elasticity or coefficient of thermalexpansion, equivalent to that of the local human bone.

Stem 22 provides excellent three-dimensional anchorage to the bone, andinduces three-dimensional loading stress conditions as close as possibleto the natural conditions. The improved stress field distribution at theinterface between the prosthesis and the bone helps prevent lysis. Thestress field set up by the prosthesis inside the bone helps induceregeneration and strengthening of the bone.

Acetabulum interface 18 and outer layer 26 of stem 22 are preferablymade of a resilient material compatible with human tissue, such aspolyurethane, which helps distribute stresses optimally, therebystimulating regeneration of bone. In accordance with a preferredembodiment of the present invention, acetabulum interface 18 and outerlayer 26 of stem 22 are constructed of a material, such as polyurethane,which has one or more mechanical and/or physical propertiessubstantially similar to human cartilage.

Hip joint prosthesis 10 may include a device for facilitating removal asis known in the art, such as a threaded boss or hole (both not shown).

It may sometimes be desired to limit the number of degrees of freedom ofthe hip joint or the range of a particular degree of freedom of movementof the femur with respect to the acetabulum, depending on the needs ofthe patient. It may also be desired to provide safeguards tosubstantially prevent dislocation of the joint. In accordance with apreferred embodiment of the present invention, apparatus is provided toachieve these goals, as is now described.

Reference is now made additionally to FIGS. 4-6. In accordance with apreferred embodiment of the present invention, artificial femoral head12 is provided with an upper delimiting rail 30 and a lower delimitingrail 32. Upper delimiting rail 30 slides in a channel 34 in artificialacetabulum 16. Channel 34 is oriented generally forwards and rearwardswith respect to the human body. As seen in FIG. 5, upper delimiting rail30 slides forwards in channel 34 when the femur is moved backwards. Itis appreciated that upper delimiting rail 30 slides backwards in channel34 when the femur is moved forwards.

Lower rail 32 slides in a channel 36 in artificial femoral socket 20. Asseen in FIG. 4, as the femur is moved laterally away from the body,lower rail 32 slides in channel 36 of socket 20 and butts thereagainst.Upper delimiting rail 30 is similarly constrained to slide in channel34. Constraining the travel of rails 30 and 32 in channels 34 and 36,respectively, substantially prevents overtravel of the femur andsubstantially prevents dislocation of artificial femoral head 12 fromartificial acetabulum 16 and artificial femoral socket 20. Moreover,since femoral head 12 is preferably constructed of a shock absorbing orresilient material, the butting of rails 30 and 32 against channels 34and 36, respectively, is substantially cushioned and damped.

Variations of hip joint prosthesis 10 are possible within the scope-ofthe present invention. Reference is now made to FIGS. 7A and 7B whichillustrate an artificial femoral head 40, constructed and operative inaccordance with another preferred embodiment of the present invention.Artificial femoral head 40 may be similar in construction and operationto artificial femoral head 12 of FIGS. 2-6. Femoral head 40 differs fromfemoral head 12 in that femoral head 40 has no delimiting rails. In FIG.7A, femoral head 40 is shown articulating with an artificial acetabulum42. In FIG. 7B, femoral head 40 is shown articulating with a naturalacetabulum 44.

Reference is now made to FIGS. 8A and 8B which illustrate an artificialfemoral head 46 fixedly attached to a crown 48, constructed andoperative in accordance with yet another preferred embodiment of thepresent invention. Femoral head 46 and crown 48 may be constructed of aresilient material, such as polyurethane.

Crown 48 may be attached to an upper portion of the thigh.Alternatively, as shown in FIG. 8A, crown 48 may be attached to a stem49. Stem 49 may include a core 49A and an outer layer 49B. Core 49A maybe of solid construction, and additionally or alternatively, may includeat least one hollow portion. Outer layer 49B may be constructed of amaterial with properties similar to human cartilage.

In FIG. 8A, femoral head 46 articulates with an artificial acetabulum50. Femoral head 46 may have an upper delimiting rail (not shown) whicharticulates with a corresponding groove (not shown) in artificialacetabulum 50. Alternatively, femoral head 46 may have a delimitinggroove with which articulates a corresponding rail in artificialacetabulum 50.

In FIG. 8B, femoral head 46 articulates with a natural acetabulum 52.Femoral head 46 may include a hollow portion (not shown), as describedhereinabove for artificial femoral head 12 with respect to FIGS. 2-6.

Alternatively, in accordance with another preferred embodiment of thepresent invention, artificial femoral head 46 may be fixedly attached toartificial acetabulum 50. In such an embodiment, artificial femoral head46 may articulate with crown 48.

Reference is now made to FIG. 8C which illustrates an artificial,self-articulating femoral head 55 fixedly attached to a stem 56 and toan artificial acetabulum 57, constructed and operative in accordancewith a preferred embodiment of the present invention. Femoral head 55 ispreferably constructed of a resilient material, such as polyurethane.Artificial acetabulum 57 may have any suitable shape, typically beinggenerally shell-shaped or spherical.

Articulation of the thigh with the innominate bone is not achieved byarticulation of femoral head 55 with artificial acetabulum 57, butrather is achieved by the self-articulation of femoral head 55.“Self-articulation” is defined as the ability of femoral head 55 topermit rotary and translatory motion of the thigh with respect to theinnominate bone due to the resilient and elastic properties andconfiguration of femoral head 55. Stem 56 may comprise an outer layer 58which may have properties similar to human cartilage.

Reference is now made to FIGS. 9A and 9B which illustrate an artificialfemoral head 60 and an artificial acetabulum 62, constructed andoperative in accordance with still another preferred embodiment of thepresent invention. Artificial femoral head 60 has one delimiting rail 64which articulates with a generally elliptically shaped recess 66 inartificial acetabulum 62. It is appreciated that this type of rail maybe employed in any of the other artificial femoral heads describedherein, either as an upper rail or a lower rail or both.

Artificial femoral head 60 may be provided with one or more fluidpassageways 67, as seen in FIG. 9A, for flow therethrough of a fluid(not shown), such as synovial fluid. It is appreciated that any of theartificial femoral heads of the present invention may be provided withfluid passageways. Fluid passageways 67 help lubricate artificialfemoral head 60, and provide damping.

Reference is now made to FIG. 9C which illustrates a flexible and stablebone connector 450, constructed and operative in accordance with apreferred embodiment of the present invention. Connector 450 preferablyincludes a hollow, generally tubular portion 452 and a bone interfaceportion 454. Interface portion 454 is preferably shaped to snugly fitthe inner geometry of the bone into which it is placed. The innergeometry of the bone may be determined by such methods as a computertomography, and interface portion 454 may then be machined accordingly.

In accordance with a preferred embodiment of the present invention,interface portion 454 has a fluted shape with a plurality of protrudingfins 456. The fluted shape of interface portion 454 and the hollownessof tubular portion 452 promote bone development and growth afterimplanting the prosthesis. Connector 450 may be fashioned in a varietyof configurations, such as straight, curved, cylindrical or tapered, forexample.

A known problem associated with the repair of broken bones and with theinsertion of stems of femoral prostheses into femurs, is that the bonemay have a curvature which changes along the length thereof in threedimensions. It is difficult to match the curvature of the stem of theprosthesis to the natural curvature of the bone. In practice, usually aset of standardized connecting pins or prostheses are used and theclosest matching prosthesis is selected and further machined or filed inthe operating theater to match the measured natural curvature of thefemur. Even with this method, gaps are almost inevitable between theprosthesis and the inner bone tissue.

It is a particular feature of the present invention that connector 450is sufficiently flexible so that it can be inserted into a bored portionof the bone, such as a femur, and deform to adapt to the changingcurvature of the bone, thereby helping to solve the aforementionedproblem. Connector 450 is preferably constructed of a material whichprovides flexibility to permit insertion into the bone, while at thesame time providing sufficient structural stability once connector 450is in place. A suitable material is one having a non-linear,“half-bell-shaped” stress-strain relationship, for example, a plasticsuch as polyurethane. The material may be reinforced with fibers, whosedensity and orientation may be selected in accordance with a particularengineering requirement.

Reference is now made to FIGS. 9D and 9E which illustrate a flexible andstable bone connector stem 460 of a hip joint prosthesis, constructedand operative in accordance with a preferred embodiment of the presentinvention. Stem 460 may be readily employed in any of the femoralprostheses of the present invention.

Stem 460 is preferably constructed similarly to connector 450, andpreferably includes a fluted elongated portion 462 having a hollowportion 464 and a plurality of protruding fins 466. A force transferelement 468, such as a wire, rod or cable, with a plurality of bulges470 is preferably disposed in hollow portion 464. Element 468 may bemade of any suitable stiff, biocompatible material, such as DYNEEMA.

Stem 460 is preferably inserted into the femur in the orientation shownin FIG. 9D. After insertion, element 468 is then moved generally in thedirection of an arrow 472, thereby causing bulges 470 to deform flutedportion 462, as seen in FIG. 9D, and fix stem 460 firmly in the femur.

Reference is now made to FIGS. 9F and 9G which illustrate a flexible andstable bone connector stem 480 of a hip joint prosthesis, constructedand operative in accordance with another preferred embodiment of thepresent invention. Stem 480 may also be readily employed in any of thefemoral prostheses of the present invention.

Stem 480 preferably includes a fluted elongated portion 482 in which isdisposed a sleeve 484 having a plurality of bulges 486. Disposed insidesleeve 484 is hollow shaft 488. Sleeve 484 is arranged for sliding,axial motion with respect to fluted portion 482 and shaft 488.

As describe hereinabove for fluted portion 462, fluted portion 482 issufficiently flexible so that it can be inserted into a bored portion ofa femur and deform to adapt to the changing curvature of the femur.

Stem 480 is preferably inserted into the femur in the orientation shownin FIG. 9F. After insertion, sleeve 484 is then moved generally in thedirection of an arrow 490, thereby causing bulges 486 to deform flutedportion 482, as seen in FIG. 9D, and fix stem 480 firmly in the femur.

Artificial femoral head 12 shown in FIGS. 2-6, has a hollow core 14.Reference is now made to FIG. 10 which illustrates a non-hollowartificial femoral head 70, constructed and operative in accordance witha preferred embodiment of the present invention. Artificial femoral head70 may include an upper rail 72 and a lower rail 74.

Reference is now made to FIG. 11 which illustrates an artificial femoralhead 80, constructed and operative in accordance with another preferredembodiment of the present invention. Femoral head 80 comprises aplurality of hollow portions 82.

Reference is now made to FIG. 12 which illustrates an artificial femoralhead 90, constructed and operative in accordance with yet anotherpreferred embodiment of the present invention. Femoral head 90 comprisesa plurality of hollow portions 92 filled with a fluid, such as synovialfluid. Additionally or alternatively, one or more fluid passageways 94may be provided. The fluid in portions 92 or passageways 94 may enhancethe shock absorbing and damping characteristics of femoral head 90.

Reference is now made to FIG. 13 which illustrates an artificial femoralhead 100, constructed and operative in accordance with still anotherpreferred embodiment of the present invention. Femoral head 100comprises a plurality of portions 102, each portion 102 not necessarilyhaving the same mechanical or physical properties. Portions 102 may beused to enhance, to optimize or to customize the shock absorbing anddamping characteristics of femoral head 100.

Reference is now made to FIG. 14A which illustrates an artificialfemoral head 110, constructed and operative in accordance with anotherpreferred embodiment of the present invention. Femoral head 110comprises a protruding delimiting bumper 112 instead of a delimitingrail.

Reference is now made to FIG. 14B which illustrates an artificialfemoral head 113, constructed and operative in accordance with yetanother preferred embodiment of the present invention. Femoral head 113comprises a thin, resilient outer shell 114 and a resilient core 115.Shell 114 may be constructed of DYNEEMA high performance polyethylenefibers, commercially available from DSM, Netherlands. DYNEEMA,particularly in the form of a woven fabric, provides a combination ofhigh strength with excellent shock absorbing and dampingcharacteristics, as well as being biocompatible. Core 115 may also bemade of DYNEEMA with properties engineered to meet requirements such asstrength or resilience, for example, and may be impregnated with othermaterials, such as a resin.

Reference is now made to FIG. 15 which illustrates an artificial femoralhead 120, constructed and operative in accordance with a preferredembodiment of the present invention. Femoral head 120 includesdelimiting grooves 122 which articulate with corresponding rails (notshown) in an artificial acetabulum and an artificial socket (not shown).

Reference is now made to FIG. 16 which illustrates an artificial femoralhead 130, constructed and operative in accordance with another preferredembodiment of the present invention. Femoral head 130 has fluidpassageways 132 which allow flow therethrough of a fluid, preferablysynovial fluid, the natural lubrication fluid of the human body. Fluidpassageways 132 may be configured in a variety of orientations,configurations and sizes. Alternatively or additionally, passageways 132may be provided in an artificial femoral socket 134 or an artificialacetabulum 136.

Fluid flowing in fluid passageways 132 may help lubricate femoral head130. The presence of fluid in fluid passageways 132 may also enhance theshock absorbing and damping characteristics of femoral head 130.

As mentioned above, the ligaments connecting the femur and theinnominate bone may be removed in the prior art, before placement of ahip joint prosthesis This is unfortunate because these ligaments areamongst the strongest ligaments in the body. These ligaments strengthenthe joint and help prevent dislocation. Preserving some or all of theligaments is therefore desirable.

Reference is now made to FIG. 17 which illustrates an artificial femoralhead 140, constructed and operative in accordance with yet anotherpreferred embodiment of the present invention. Artificial femoral head140 is preferably relatively small in size, thereby helping to reducethe need for tampering with some of the hip joint ligaments. In thisembodiment, femoral head 140 articulates with an artificial acetabulum142 and an artificial socket 144. Socket 144 may be attached directly tothe femur without a stem, such as by bonding or via a crown (not shown)similar to the crown-shaped portion 20B described hereinabove withreference to FIGS. 2 and 3.

By eliminating the stem, the need for tampering with or drilling intothe femur may also be eliminated. There may be no need to remove theentire natural femoral head, but rather a portion thereof may bepreserved. Preserving part of the femur may simplify the surgicaloperation and may preserve most of the strength of the bone.

The need for tampering with some of the ligaments may also be reduced.Indeed, the intact ligaments themselves act together with the prosthesisof FIG. 17, because they tend to keep femoral head 140 properlyinstalled. In addition, the embodiment of FIG. 17 may be more easily andquickly implanted than prostheses having stems.

Other embodiments of the present invention which address the problem ofpreserving the hip joint ligaments are described hereinbelow withrespect to FIGS. 19A-21.

Reference is now made to FIGS. 18A and 18B which illustrate anartificial femoral head 150, constructed and operative in accordancewith another preferred embodiment of the present invention. Femoral head150 comprises a plurality of alternating adjacent portions 152 and 154of substantially rigid and substantially resilient materialsrespectively. The rigid material is preferably a composite material andthe resilient material is preferably polyurethane. In accordance with apreferred embodiment of the present invention, femoral head 150 isattached to an artificial acetabulum 156.

The material composition and the geometry of the portions 152 and 154may be optimized to provide the desired rigidity and resiliency. In thismanner, femoral head 150 may be constructed as a non-linear spring withmultiple spring constants.

Femoral head 150 may have different rigidity and resiliency forforward-backward motion as opposed to lateral motion. For example, asseen in FIG. 18B, adjacent portions 152 and 154 are generallyomega-shaped. Such a shape permits relatively easy swinging of the femurforwards and backwards with respect to the body, while at the same timeconstraining the swinging range to prevent overtravel of the femur. Theresiliency of femoral head 150 damps the motion of the femur at thelimits of its swing. The omega shape is stiffer in the lateraldirection, thus limiting lateral motion of the femur with respect to thebody. It is appreciated that femoral head 150 may be alternativelyconstructed to allow greater freedom of motion laterally than forwardsand backwards.

Reference is now made to FIGS. 18C and 18D which show femoral heads 160and 162 respectively, with adjacent layers 161 and 163 of substantiallyrigid and substantially resilient materials, respectively, constructedand operative in accordance with an alternative preferred embodiment ofthe present invention. As shown in FIGS. 18E and 18F, femoral heads 160and 162 may be provided with apertures 164 and 166 respectively, whichmay, for example, provide a passageway for synovial fluid, nerves, bloodvessels, ligaments, tissues, elongated force transmitting members orprosthetic controls. Fluid in apertures 164 and 166 may enhance thedamping of femoral heads 160 and 162 respectively.

It is appreciated that the embodiments of FIGS. 18A-18F may be used ashinge or joint elements in other applications where it is desired toprovide different rigidity or resiliency in different directions ofmotion.

Reference is now made to FIG. 180 which illustrates an artificialacetabulum 400, constructed and operative in accordance with a preferredembodiment of the present invention.

Artificial acetabulum 400 preferably includes an interface 402 made of aresilient, cartilage-like material, and preferably has a generallytriangular cut-out 404. Acetabulum 400 preferably also includes an outerridge 406 that “snap-fits” into the natural acetabulum socket, therebysubstantially fixing artificial acetabulum 400 in the natural socket.The natural acetabulum may have to be drilled, cut or otherwise machinedto ensure a proper snap fit so that acetabulum 400 is rigidly held inplace. Ridge 406 may be continuous or may be formed of discrete portionsthat protrude into the natural acetabulum recesses. As seen in FIG. 18G,interface 402 may comprise a deformable, resilient flange 408 withexpandable, accordion-like folds. Interface 402 may be one highlydeformable piece, or may be slightly deformable, in which case it mayfit into the natural acetabulum with a slight “click”.

It is a particular feature of the present invention that ridge 406provides shock absorption and positively locks interface 402 into arecess prepared in the natural socket, without any need for screws oradhesive. Interface 402 may comprise one or more layers. The largesurface area of interface 402 provides a large load bearing and shockabsorbing surface for a femoral head. Interface 402 may itself serve asan articulating surface for a femoral head, in which case the largesurface area diminishes fretting and wearing of the articulatingsurfaces.

Reference is now made to FIGS. 18K and 18L which illustrate a crosssection of interface 402 constructed in accordance with two preferredembodiments of the present invention. In FIG. 18K, it is seen thatinterface 402 preferably includes a plurality of protrusions 410 forlocking interface 402 in recesses prepared in the natural socket. Asseen in FIGS. 18G and 18L, interface 402 may also include an “umbilical”protrusion 412 that is configured to fit the natural or restructured“umbilical” recess of the natural acetabulum. This allows reduction ofmachining of the innominate bone and leaves a stronger bone.

Acetabulum 400 also preferably includes a locking piece 414complementary shaped and sized to snugly fit into triangular cut-out404. Interface 402 together with locking piece 414 may be used as thearticulating portion of the prosthesis with the femur. Additionally,there is preferably provided an articulation portion 416 which snapstogether with a recess 418 formed in interface 402. Articulation portion416 may be made of metal, composite material, cartilage-like material,polyurethane or DYNEEMA. Articulation portion 416 may alternatively beattached to interface 402 by means of a bayonet type of connection orsimply a press fit without clicking. Articulating portion 416 makesartificial acetabulum 400 into one stable integral assembly which iseasily assembled in and removed from the innominate bone.

Reference is now made to FIGS. 18H, 18I and 18J which illustrateinstalling artificial acetabulum 400 into a natural acetabulum, inaccordance with a preferred embodiment of the present invention. In FIG.18H, an insertion tool 420 squeezes triangular cut-out 404 inwardly inthe direction of arrows 422, to allow insertion of interface 402 intothe natural socket. Upon release of insertion tool 420, cut-out 404springs outwards much in the manner of a retaining ring, therebypressing interface 402 firmly against and into the natural socket.Prongs of the insertion tool may be placed in prepared recesses or holesin interface 402.

In FIG. 18I, locking piece 414 is inserted into cut-out 404, therebycompleting the shape of acetabulum 400 and firmly locking interface 402into the natural socket when an articulating head or an additionalarticulating surface is assembled therewith. In FIG. 18J, articulationportion 416 is snapped together with interface 402, thereby makingartificial acetabulum 400 into one integral assembly.

As mentioned above, the ligaments connecting the femur and theinnominate bone may be removed in the prior art, before placement of ahip joint prosthesis. Methods for preserving the hip joint ligaments, orreinforcing or replacing them, are now described.

Reference is now made to FIGS. 19A-19C which illustrate a method ofincision of ligaments, such as prior to insertion of a hip jointprosthesis, in accordance with a preferred embodiment of the presentinvention. A primary goal of the method of incision is to preserve theligaments.

FIG. 19A illustrates a hip joint 170 prior to incision. As seen in FIG.19B, a wave-like incision 172 may be made, such as with a laser device,in any or all of the ilio-femoral, pubo-femoral and ischio-femoralligaments. As seen in FIG. 19C, the cut ligaments allow ample room forplacement of a hip joint prosthesis (not shown).

As is known in the art, ligaments generally contract after incision,impairing mending of the ligament tissue. The wave-like shape ofincision 172 permits slightly shifting the ligaments so that there issufficient contact or overlap of the ligaments even after contraction,thereby helping to promote stitching and mending of the ligament tissue.

Reference is now made to FIG. 20 which illustrates a sleeve 180 forjoining a femoral head 182 with the innominate bone, constructed andoperative in accordance with a preferred embodiment of the presentinvention. Sleeve 180 is preferably made of a high strength wovenfabric, such as DYNEEMA, polyethylene, nylon or polyurethane. Sleeve 180preferably comprises filaments with a high elasticity modulus in thelongitudinal direction of the ligaments, along an axis 184, and acircumferential stretching weave along an axis 186, generallyperpendicular to axis 184, as seen in FIG. 20.

Sleeve 180 also preferably includes an anchoring band 188 for attachingsleeve 180 to the innominate bone. Anchoring band 188 may be attached tothe innominate bone and sleeve 180 may be attached to the femoral headby any suitable means, such as bonding or with mechanical fasteners.Sleeve 180 may replace or assist the natural ligaments of the hip joint.Sleeve 180 may also help in mending of ligament tissue after surgery.All or portions of sleeve 180 may be constructed of a material, such asmaterial used for dissolving sutures, which eventually dissolves after apredetermined period.

The present invention also provides a hip joint prosthesis which maysubstantially reduce the need for tampering with the hip jointligaments. Reference is now made to FIG. 21 which illustrates anexpandable artificial femoral head 190, constructed and operative inaccordance with a preferred embodiment of the present invention. Femoralhead 190 is preferably constructed of a resilient material, such aspolyurethane. When expanded, femoral head 190 has substantially the sameshape as femoral head 12, described hereinabove with reference to FIGS.2 and 3.

In contrast to the prior art, femoral head 190, before expansion, may beinserted between the existing ligaments with minimum tampering thereof.Femoral head 190 may then be expanded to the desired shape. Femoral head190 may be inflated by means of a fluid (not shown) introduced, forexample, via a thin needle valve (not shown). Alternatively, femoralhead 190 may be expanded by introducing therein components of anexpandable foam (not shown), which expand inside femoral head 190.

The present invention will now be described in detail with respect to aprosthesis for a ginglymus, namely the knee joint. For a betterunderstanding of a knee joint prosthesis, a basic description of thehuman knee joint is presented here with reference to FIG. 22, whichillustrates the knee of the right leg.

The knee is a hinge comprising the internal and external condyles of thefemur which articulate with the upper end of the tibia. The femoralcondyles are separated by a deep fossa. The upper end of the tibiacomprises two tuberosities, the external of which articulates with thehead of the fibula.

The knee also comprises the trochlea of the femur (not shown in FIG. 22)which is located forward and upward of the condyles. The patella slidesalong the trochlea. The patella is shown pulled down in FIG. 22 in orderto show some of the ligaments and cartilage which connect the femur,tibia, fibula and patella. These ligaments and cartilage include, interalia, the external lateral ligament which connects the external femoralcondyle to the fibula, the internal lateral ligament which connects theinternal femoral condyle to the tibia, the ligamentum patellae to whichis attached the patella, and the transverse ligament and internalsemilunar cartilage which are attached to the head of the tibia. Thetransverse ligament, internal semilunar cartilage and the anteriorcrucial ligament are attached to the spine (not shown in FIG. 22) of thetibia. The spine is a series of elevations on the head of the tibiaopposite the fossa between the femoral condyles.

Reference is now made to FIGS. 23 and 24 which illustrate a kneeprosthesis 200, constructed and operative in accordance with a preferredembodiment of the present invention. Knee prosthesis 200 comprises anupper or femoral portion 202 and a lower or tibial portion 204, as seenin FIGS. 23 and 24.

Referring additionally to FIG. 25, it is seen that femoral portion 202preferably comprises two pads 206 upon which rest the internal andexternal condyles of the femur, as seen in FIG. 24, and a trochlearportion 208 which is intermediate the patella and the trochlea, as seenin FIG. 23. Pads 206 articulate with tibial portion 204. As seen in FIG.25, femoral portion 202 also preferably has a socket 210, whose functionis described hereinbelow with reference to tibial portion 204.

Referring additionally to FIG. 26, it is seen that tibial portion 204includes an artificial spine 212 which extends into socket 210. It isappreciated that when the knee flexes, socket 210 restricts the movementof spine 212 therein. Socket 210 and/or spine 212 are preferablyconstructed of a shock absorbing or resilient material, such that themovement of spine 212 is cushioned at the limits of travel in socket210.

As seen in FIG. 23, spine 212 may extend beyond socket 210 into thefossa of the femur. Tibial portion 204 also preferably has twodepressions 214 with which pads 206 may articulate. Tibial portion 204preferably includes a stem 216 for attachment to the tibia. Tibialportion 204 may have one or more hollow portions 218 to increase shockabsorption, damping or resiliency.

As seen in FIG. 23, a tibial cushion 220 may be placed intermediatetibial portion 204 and the head of the tibia, tibial cushion 220preferably being constructed of a material compatible with human tissue,such as polyurethane. In accordance with a preferred embodiment of thepresent invention, femoral portion 202 may be constructed of asubstantially rigid material, such as a composite material, and tibialportion 204 may be constructed of a substantially resilient material,such as polyurethane.

In accordance with another preferred embodiment of the presentinvention, femoral portion 202 may be constructed of a substantiallyresilient material and tibial portion 204 may be constructed of asubstantially rigid material.

In accordance with yet another preferred embodiment of the presentinvention, femoral portion 202 may be constructed of a substantiallyresilient material and tibial portion 204 may be constructed of asubstantially resilient material.

It is appreciated that knee prosthesis 200 is operative to absorb staticand dynamic shocks.

It is a particular feature of the present invention that the resiliencyof either femoral portion 202 or tibial portion 204 allows theconfiguration of the contact surfaces between portions 202 and 204 tochange according to physical factors, such as load or motion. Forexample, when bearing loads directed downwards on the tibia, the contactarea between portions 202 and 204 becomes relatively large, therebyincreasing stability and decreasing pressure on the tibia. When the kneeflexes, the contact area is relatively small, which facilitates motionof the tibia with respect to the femur. Femoral portion 202 and tibialportion 204 have different radii of curvature when not exposed toforces. The radii of curvature approach equality when bearing forcesdirected downwards on the tibia.

Reference is now made to FIGS. 27 and 28 which illustrate a kneeprosthesis 230, constructed and operative in accordance with anotherpreferred embodiment of the present invention. Knee prosthesis 230comprises an upper or femoral portion 232 and a lower or tibial portion234, as seen in FIGS. 27 and 28. Tibial portion 234 is substantiallyidentical to tibial portion 204 described hereinabove with reference toFIGS. 23, 24 and 26.

Femoral portion 232 preferably comprises two pads 236 upon which restthe internal and external condyles of the femur, as seen in FIG. 28, anda trochlear portion 238 which is intermediate the patella and thetrochlea, as seen in FIG. 27. Pads 236 articulate with tibial portion234. Pads 236 preferably have one or more hollow portions 240, and mayhave one or more fluid passageways 242, for permitting flow therethroughof synovial fluid, thereby providing lubrication and enhancing the shockabsorbing and damping characteristics of knee prosthesis 230.

Femoral portion 232 articulates with tibial portion 234 of kneeprosthesis 230 by sliding along the generally concave surface of tibialportion 234. Reference is now made to FIGS. 29 and 30 which illustrate aknee prosthesis 250, constructed and operative in accordance withanother preferred embodiment of the present invention. Knee prosthesis250 comprises an upper or femoral portion 252 and a lower or tibialportion 254, as seen in FIGS. 29 and 30. Femoral portion 252 ispreferably generally convex and articulates with tibial portion 254 byrolling along the generally convex surface of tibial portion 254.

As described hereinabove with reference to FIG. 23, the resiliency ofeither femoral portion 252 or tibial portion 254 allows theconfiguration of the contact surfaces between portions 252 and 254 tochange according to physical factors, such as load or motion.

Reference is now made to FIGS. 31 and 32 which illustrate a kneeprosthesis 260, constructed and operative in accordance with anotherpreferred embodiment of the present invention. Knee prosthesis 260comprises an upper or femoral portion 262 which articulates with a loweror tibial portion 264 by means of one or more roller elements 266, asseen in FIGS. 31 and 32.

Portions 262 and 264 may be substantially rigid and roller elements 266may be substantially resilient. Conversely, portions 262 and 264 may besubstantially resilient and roller elements 266 may be substantiallyrigid.

Roller elements 266 may permit articulation of femoral portion 262 withtibial portion 264 by means of rolling, sliding, a combination ofrolling and sliding, or rolling combined with a deformation of one ormore of roller elements 266. Roller elements 266 may be formed in anyshape which provides such rolling and sliding, such as being generallycylindrical in shape. An alternative shape is shown in FIG. 33.

At least one fluid passageway 268 may be provided in each roller element266 for passage therethrough of a fluid, such as synovial fluid, therebyproviding lubrication and enhancing the shock absorbing and dampingcharacteristics of knee joint prosthesis 260.

Alternatively or additionally, each roller element 266 may have at leastone hollow portion. Alternatively or additionally, each roller element266 may comprise a plurality of portions, each portion not necessarilyhaving the same mechanical or physical properties. These portions may beused to enhance, to optimize or to customize the shock absorbing anddamping characteristics of the roller element 266.

Femoral portion 262 may be attached directly to the femoral condyles.Alternatively, as shown in FIG. 32, a femoral pad 270 may be placedintermediate femoral portion 262 and the femoral condyles. Femoral pad270 may be constructed of a material with properties similar to humancartilage, such as polyurethane.

Reference is now made to FIG. 34 which illustrates a bone fastener 300for fastening bone fractures, constructed and operative in accordancewith a preferred embodiment of the present invention.

Bone fastener 300 preferably includes a core 302 and an outer layer 304.Outer layer 304 preferably includes one or more ridges 306, which, interalia, help distribute stresses and help fasten bone fastener 300 to abone. Core 302 may be of solid or hollow construction. Bone fastener 300may have any suitable cross sectional shape, such as circular orelliptical.

In accordance with a preferred embodiment of the present invention, core302 is preferably constructed of a rigid material, for example,stainless steel or a structural plastic. Alternatively, the rigidmaterial may be a composite material, such as graphite fibers, which maybe constructed to have mechanical or physical properties, such asmodulus of elasticity or coefficient of thermal expansion, equivalent tothat of the local human bone.

Outer layer 304 is preferably made of a resilient material compatiblewith human tissue, such as polyurethane, which helps distribute stressesoptimally, thereby stimulating regeneration of bone. In accordance witha preferred embodiment of the present invention, outer layer 304 isconstructed of a material, such as polyurethane, which has one or moremechanical and/or physical properties substantially similar to humancartilage.

Reference is now made to FIG. 35 which illustrates a vertebrareplacement 310, constructed and operative in accordance with apreferred embodiment of the present invention.

Vertebra replacement 310 preferably includes at least one inner member312, at least one intermediate member 314 and at least one outer member316. Inner member 312 is preferably constructed of a substantiallyresilient material and may have one or more hollow portions 318.Alternatively, portions 318 may be filled with a fluid, such as synovialfluid. Additionally or alternatively, a fluid passageway (not shown) maybe provided for fluid flow therethrough, thereby providing lubricationand enhancing the shock absorbing and damping characteristics ofvertebra replacement 310.

Intermediate portion 314 may be less flexible than inner member 312, andis preferably constructed of a rigid material, for example, stainlesssteel or a structural plastic. Alternatively, the rigid material may bea composite material, such as graphite fibers, which may be constructedto have mechanical or physical properties, such as modulus of elasticityor coefficient of thermal expansion, equivalent to that of the localhuman bone.

Outer members 314 are preferably made of a resilient material compatiblewith human tissue, such as polyurethane, which helps distribute stressesoptimally. In accordance with a preferred embodiment of the presentinvention, outer members 314 may be constructed of a material, such aspolyurethane, which has one or more mechanical and/or physicalproperties substantially similar to human cartilage.

In accordance with a preferred embodiment of the present invention,geometrical data may be provided, such as by computerized tomography,and be used to prepare and select an optimal prosthesis or bone fastenerprior to surgery. Data input, such as from the results of computerizedtomography, may be used to match the geometry of the prosthesis or bonefastener to the needs of the patient. Either the prosthesis or the bone,or both, may be shaped, such as by computerized machining, using thegeometrical data obtained.

Alternatively, the geometry of a preformed, standard prosthesis may beused to reshape the bone to match the prosthesis. Alternatively, thegeometrical data used to reshape the bone may be used generally to formthe prosthesis in real time.

It is appreciated that various features of the invention which are, forclarity, described in the contexts of separate embodiments may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention which are, for brevity, described in thecontext of a single embodiment may also be provided separately or in anysuitable subcombination.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed hereinabove. Rather, the scope of the present invention isdefined only by the claims that follow:

1. A hip joint prosthesis comprising: an artificial acetabular devicefor securely engaging an artificial femur; the device comprising atleast one resilient element formed of a compatible plastic, in agenerally cup-shaped configuration defining an articulating surface forarticulating engagement with a femoral head; and a mounting surface formounting engagement with a machined natural acetabulum, said mountingsurface comprising a mounting surface portion configured for snap fitengagement with a correspondingly machined natural acetabulum surfaceportion defined by said machined natural acetabulum.
 2. A hip jointprosthesis comprising: an artificial acetabular device for securelyengaging an artificial femur; the device comprising at least oneresilient element formed of a compatible plastic, in a generallycup-shaped configuration defining an articulating surface forarticulating engagement with a femoral head and a mounting surface formounting engagement with a machined natural acetabulum, said mountingsurface comprising a mounting surface portion configured for snap fitengagement with a correspondingly machined natural acetabulum surfaceportion defined by said machined natural acetabulum wherein saidarticulating surface and said mounting surface of rotation lie generallyparallel to each other.
 3. A hip joint prosthesis a comprising anartificial acetabular device for securely engaging an artificial femur;the device comprising at least one resilient element formed of acompatible plastic, in a generally cup-shaped configuration defining anarticulating surface for articulating engagement with a femoral head anda mounting surface for mounting engagement with a machined naturalacetabular, said mounting surface comprising a mounting surface portionconfigured for snap fit engagement with a correspondingly machinednatural acetabulum surface portion defined by said machined naturalacetabulum; said mounting surface portion comprising at least oneprotrusion.
 4. A hip joint prosthesis comprising an artificialacetabular device for securely engaging an artificial femur; the devicecomprising at least one resilient element formed of a compatibleplastic, in a generally cup-shaped configuration defining anarticulating surface for articulating engagement with a femoral head anda mounting surface for mounting engagement with a machined naturalacetabulum, said mounting surface comprising a mounting surface portionconfigured for snap fit engagement with a correspondingly machinednatural acetabulum surface portion defined by said machined naturalacetabulum; said at least one protrusion comprising a generallyperipherally extending protrusion.
 5. A hip joint prosthesis comprisingan artificial acetabular device for securely engaging an artificialfemur; the device comprising at least one resilient element formed of acompatible plastic, in a generally cup-shaped configuration defining anarticulating surface for articulating engagement with a femoral head anda mounting surface for mounting engagement with a machined naturalacetabulum; said mounting surface comprising a mounting surface portionconfigured for snap fit engagement with a correspondingly machinednatural acetabulum surface portion defined by said machined naturalacetabulum; said mounting surface portion defining an undercut.
 6. A hipjoint prosthesis comprising: an artificial acetabular device forsecurely engaging an artificial femur; the device comprising at leastone, resilient element formed of a compatible plastic, in a generallycup-shaped configuration defining an articulating surface forarticulating engagement with a femoral head; and a mounting surface formounting engagement with a machined natural acetabulum, said mountingsurface comprising a mounting surface having an outer ridge portionconfigured for snap fit engagement with a correspondingly machinednatural acetabulum surface portion defined by said machined naturalacetabulum.
 7. A hip joint prosthesis comprising: an artificialacetabular device for securely engaging an artificial femur; the devicecomprising at least one resilient element formed of a compatibleplastic, in a generally cup-shaped configuration defining anarticulating surface for articulating engagement with a femoral head anda mounting surface for mounting engagement with a machined naturalacetabular, said mounting surface comprising a mounting surface havingan outer ridge portion configured for snap fit engagement with acorrespondingly machined natural acetabulum surface portion defined bysaid machined natural acetabulum wherein said articulating surface andsaid mounting surface of rotation lie generally parallel to each other.8. A hip joint prosthesis comprising an artificial acetabular device forsecurely engaging an artificial femur; the device comprising at leastone resilient element formed of a compatible plastic, in a generallycup-shaped configuration defining an articulating surface forarticulating engagement with a femoral head and a mounting surface formounting engagement with a machined natural acetabulum; said mountingsurface comprising a mounting surface having an outer ridge portionconfigured for snap fit engagement with a correspondingly machinednatural acetabulum surface portion defined by said machined naturalacetabulum, said mounting surface portion comprising at least oneprotrusion.
 9. A hip joint prosthesis comprising an artificialacetabular device for securely engaging an artificial femur; the devicecomprising at least one, resilient element formed of a compatibleplastic, in a generally cup-shaped configuration defining anarticulating surface for articulating engagement with a femoral head anda mounting surface for mounting engagement with a machined naturalacetabulum, said mounting surface comprising a mounting surface havingan outer ridge portion configured for snap fit engagement with acorrespondingly machined natural acetabulum surface portion defined bysaid machined natural acetabulum; said at least one protrusioncomprising a generally peripherally extending protrusion.
 10. A hipjoint prosthesis comprising an artificial acetabular device for securelyengaging an artificial femur; the device comprising at least oneresilient element formed of a compatible plastic, in a generallycup-shaped configuration defining an articulating surface forarticulating engagement with a femoral head and a mounting surface formounting engagement with a machined natural acetabulum; said mountingsurface comprising a mounting surface having an outer ridge portionconfigured for snap fit engagement with a correspondingly machinednatural acetabulum surface portion defined by said machined naturalacetabulum; said mounting surface portion defining an undercut.
 11. Ahip joint prosthesis comprising: an artificial acetabular device forsecurely engaging an artificial femur; the device comprising at leastone resilient element formed of a compatible polyurethane, in agenerally cup-shaped configuration defining an articulating surface forarticulating engagement with a femoral head; and a mounting surface formounting engagement with a machined natural acetabulum, said mountingsurface comprising a mounting surface portion configured for snap fitengagement with a correspondingly machined natural acetabulum surfaceportion defined by said machined natural acetabulum.
 12. A hip jointprosthesis comprising: an artificial acetabular device for securelyengaging an artificial femur; the device comprising at least one elementformed of a compatible polyurethane, in a generally cup-shapedconfiguration defining an articulating surface for articulatingengagement with a femoral head and a mounting surface for mountingengagement with a machined natural acetabulum, said mounting surfacecomprising a mounting surface portion configured for snap fit engagementwith a correspondingly machined natural acetabulum surface portiondefined by said machined natural acetabulum wherein said articulatingsurface and said mounting surface of rotation lie generally parallel toeach other.
 13. A hip joint prosthesis comprising an artificialacetabular device for securely engaging an artificial femur; the devicecomprising at least one, resilient element formed of a compatiblepolyurethane, in a generally cup-shaped configuration defining anarticulating surface for articulating engagement with a femoral head anda mounting surface for mounting engagement with a machined naturalacetabulum; said mounting surface comprising a mounting surface portionconfigured for snap fit engagement with a correspondingly machinednatural acetabulum surface portion defined by said machined naturalacetabular; said at least one protrusion comprising a generallyperipherally extending protrusion.
 14. A hip joint prosthesis comprisingan artificial acetabular device for securely engaging an artificialfemur; the device comprising at least one, resilient element formed of acompatible polyurethane, in a generally cup-shaped configurationdefining an articulating surface for articulating engagement with afemoral head and a mounting surface for mounting engagement with amachined natural acetabular; said mounting surface comprising a mountingsurface portion configured for snap fit engagement with acorrespondingly machined natural acetabulum surface portion defined bysaid machined natural acetabulum; said at least one protrusion definingan undercut.
 15. A hip joint prosthesis comprising: an artificialacetabular device for securely engaging an artificial femur; the devicecomprising at least one resilient element formed of a compatiblepolyurethane, in a generally cup-shaped configuration defining anarticulating surface for articulating engagement with a femoral head;and a mounting surface for mounting engagement with a machined naturalacetabulum, said mounting surface comprising a mounting surface havingan outer ridge portion configured for snap fit engagement with acorrespondingly machined natural acetabulum surface portion defined bysaid machined natural acetabulum.
 16. A hip joint prosthesis comprising:an artificial acetabular device for securely engaging an artificialfemur; the device comprising at least one resilient element formed of acompatible polyurethane, in a generally cup-shaped configurationdefining an articulating surface for articulating engagement with afemoral head and a mounting surface for mounting engagement with amachined natural acetabulum, said mounting surface comprising a mountingsurface having an outer ridge portion configured for snap fit engagementwith a correspondingly machined natural acetabulum surface portiondefined by said machined natural acetabulum wherein said articulatingsurface and said mounting surface of rotation lie generally parallel toeach other.
 17. A hip joint prosthesis comprising an artificialacetabular device for securely engaging an artificial femur; the devicecomprising at least one resilient element formed of a compatiblepolyurethane, in a generally cup-shaped configuration defining anarticulating surface for articulating engagement with a femoral head anda mounting surface for mounting engagement with a machined naturalacetabulum; said mounting surface comprising a mounting surface havingan outer ridge portion configured for snap fit engagement with acorrespondingly machined natural acetabulum surface portion defined bysaid machined natural acetabular; said mounting surface portioncomprising at least one protrusion.
 18. A hip joint prosthesiscomprising an artificial acetabular device for securely engaging anartificial femur; the device comprising at least one resilient elementformed of a compatible polyurethane, in a generally cup-shapedconfiguration defining an articulating surface for articulatingengagement with a femoral head and a mounting surface for mountingengagement with a machined natural acetabulum, said mounting surfacecomprising a mounting surface having an outer ridge portion configuredfor snap fit engagement with a correspondingly machined naturalacetabulum surface portion defined by said machined natural acetabulum;said at least one protrusion comprising a generally peripherallyextending protrusion.
 19. A hip joint prosthesis an artificialacetabular device for securely engaging an artificial femur; the devicecomprising at least one resilient element formed of a compatiblepolyurethane, in a generally cup-shaped configuration defining anarticulating surface for articulating engagement with a femoral head anda mounting surface for mounting engagement with a machined naturalacetabulum; said mounting surface comprising a mounting surface havingan outer ridge portion configured for snap fit engagement with acorrespondingly machined natural acetabulum surface portion defined bysaid machined natural acetabulum; said mounting surface portion definingan undercut.
 20. A hip joint prosthesis comprising an artificialacetabular assembly for tightly engaging and articulating an artificialfemur replacement portion, the assembly comprising: (i) a resilientelement formed of a compatible plastic, in a generally cup-shapedconfiguration defining a mounting surface portion for mountingengagement with a machined natural acetabulum said mounting surfacecomprising a mounting surface portion configured for snap fit engagementwith a correspondingly machined natural acetabulum surface portiondefined by said machined natural acetabulum; and (ii) a rigid generallyparallel cup-shaped element securely interlocking with said resilientelement having an opposite surface portion for articulating engagementwith a femoral head; said element being selected from the groupconsisting of metal, composite material cartilage like material,polyurethane, and DYNEEMA.